The present invention relates to subterranean cementing operations, and more particularly, to methods and systems for reverse-circulation cementing in subterranean formations.
Hydraulic cement compositions commonly are utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings, such as casings and liners, are cemented in well bores. In performing primary cementing, hydraulic cement compositions commonly are pumped into an annular space between the walls of a well bore and the exterior surface of a pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming therein an annular sheath of hardened, substantially impermeable cement that substantially supports and positions the pipe string in the well bore, and that bonds the exterior surface of the pipe string to the walls of the well bore. Conventionally, two pumping methods have been used to place the cement composition in the annulus. First, the cement composition may be pumped down the inner diameter of the pipe string, out through a casing shoe and/or circulation valve at the bottom of the pipe string, and up through the annulus to a desired location. The direction in which the cement composition is pumped in this first method is called a conventional-circulation direction. Second, the cement composition may be pumped directly down the annulus, thereby displacing any well fluids present in the annulus by pushing them through the casing shoe and up the inner diameter of the pipe string. The direction in which the cement composition is pumped in this second method is called a reverse-circulation direction.
In reverse-circulation direction applications, it is sometimes undesirable for the cement composition to enter the inner diameter of the pipe string from the annulus through the casing shoe and/or circulation valve. For example, if an excessive volume of cement composition is permitted to enter the inner diameter of the pipe string, the cement composition may rise to a level equal to that of a hydrocarbon-bearing zone intended to be perforated. This may be problematic because it may prevent the subsequent placement of tools (e.g., perforating equipment) adjacent the hydrocarbon-bearing zone, which may prevent the perforation of the zone and subsequent production of hydrocarbons therefrom, unless the excess cement is drilled out. Accordingly, whenever a cement composition that is reverse-circulated into a subterranean annulus enters the inner diameter of the pipe string, the excess cement composition in the pipe string typically is drilled out before further operations are conducted. The drill-out procedure often requires additional time, labor, and expense that may be avoided by preventing the excess cement composition from entering the inner diameter of the pipe string through the casing shoe and/or circulation valve.